package com.meteor.dao;

import java.io.IOException;
import java.io.InputStream;
import java.sql.*;
import java.util.Properties;

//操作数据库的公共类
public class BaseDao {
    private static final String driver;
    private static final String url;
    private static final String username;
    private static final String password;

    //静态代码块，随着类的加载而加载
    static{
        Properties properties = new Properties();
        InputStream is = BaseDao.class.getClassLoader().getResourceAsStream("db.properties");
        try {
            //properties.load()从输入字节流读取属性列表（键和元素对）。
            properties.load(is);
        } catch (IOException e) {
            e.printStackTrace();
        }
        driver = properties.getProperty("driver");
        url = properties.getProperty("url");
        username = properties.getProperty("username");
        password = properties.getProperty("password");
    }

    //获取数据库的连接
    public static Connection getConnection() {
        Connection connection = null;
        try {
            Class.forName(driver);
            //尝试建立与给定数据库URL的连接。
            connection = DriverManager.getConnection(url, username, password);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return connection;
    }

    //编写查询公共方法
    public static ResultSet execute(Connection connection,String sql,Object[] params,ResultSet resultSet,PreparedStatement preparedStatement) throws SQLException {
        //connection.prepareStatement(sql)创建一个 PreparedStatement对象，用于将参数化的SQL语句发送到数据库。
        preparedStatement = connection.prepareStatement(sql);
        for (int i = 0; i < params.length; i++) {
            preparedStatement.setObject(i+1,params[i]);//使用给定对象设置指定参数的值。
        }
        resultSet = preparedStatement.executeQuery();
        return resultSet;
    }

    //编写增删改公共方法
    public static int execute(Connection connection,String sql,Object[] params,PreparedStatement preparedStatement) throws SQLException {
        //connection.prepareStatement(sql)创建一个 PreparedStatement对象，用于将参数化的SQL语句发送到数据库。
        preparedStatement = connection.prepareStatement(sql);
        for (int i = 0; i < params.length; i++) {
            preparedStatement.setObject(i+1,params[i]);
        }
        int updateRows = preparedStatement.executeUpdate();
        return updateRows;
    }

    //释放资源
    public static boolean closeResource(Connection connection,PreparedStatement preparedStatement,ResultSet resultSet) {
        boolean flag = true;
        if(resultSet != null) {
            try {
                resultSet.close();
                //GC回收机制，如果对象为null，就会被回收。
                resultSet = null;
            } catch (SQLException e) {
                e.printStackTrace();
                flag = false;
            }
        }

        if(preparedStatement != null) {
            try {
                preparedStatement.close();
                //GC回收机制，如果对象为null，就会被回收。
                preparedStatement = null;
            } catch (SQLException e) {
                e.printStackTrace();
                flag = false;
            }
        }

        if(connection != null) {
            try {
                connection.close();
                //GC回收机制，如果对象为null，就会被回收。
                connection = null;
            } catch (SQLException e) {
                e.printStackTrace();
                flag = false;
            }
        }
        return flag;
    }
}
